Extra- and intra-articular proximal tibia malunion is not uncommon. Functional impact is variable but may lead to almost total impotence. The present study aimed to provide a review on malunion, answering 5 questions: (1) How should malunion be classified, and with what pathogenicity? Malunion results from reduction defect and/or secondary displacement in tibial plateau fracture (A2, A3, B, C on the AO classification), but also from previous epiphysiodesis or osteotomy (valgization or varization). (2) How should malunion be assessed? Pre-treatment work-up comprises standard X-ray (AP, lateral, full-length), but also 2D and 3D CT-scan to assess the severity and type of residual depression in old fracture. (3) What conservative treatments are available, and for whom? In under-50 year-olds, correction osteotomy is recommended: intra- or extra-articular or combined. In extra-articular malunion, especially in the absence of osteoarthritis, realignment osteotomy may be indicated even in elderly subjects. (4) What implants are suited to what malunion, and for whom? In over-50 year-olds with intra-or extra-articular or combined malunion, partial or total replacement is recommended, isolated or associated to realignment osteotomy. The open questions concern material removal, surgical approach and type of implant, bearing in mind that these implants raise technical difficulties. (5) What are the complications, and the results? Results with osteotomy and partial prostheses are generally satisfactory. Results in total replacement are poorer than for primary implants in osteoarthritis of the knee, with much more frequent complications. LEVEL OF EVIDENCE: V, expert opinion.